This invention relates to semiconductor pressure transducers and, more particularly, to such transducers which are formed to compensate for signals occurring at zero pressure differential.
The semiconductor pressure transducers known in the prior art employ a diaphragm responsive to the pressure differential across the two surfaces thereof. The diaphragm is formed of a single crystal semiconductor chip having stress sensors disposed on one surface thereof. Stress sensors which are widely used for this purpose exhibit a piezoresistive characteristic, whereby the resistance of the sensor varies with the stress experienced by the sensor as the stress in the chip changes with the differential pressure. A circular cavity is formed in the other surface of the chip to form the diaphragm, and a cylindrical tube has one end thereof bonded to such other surface to surround the cavity.
Normally at least one pair of radial stress sensors and one pair of circumferential stress sensors are disposed on the surface of the chip.
Originally, circular chips having circular diaphragms were employed, whereby the entire transducer was symmetrical with respect to the common axis of the tube, the cavity, and the chip. More recently however, square semiconductor chips have come to be employed because a plurality of such square chips can be readily obtained by the dicing of a crystal wafer or slice. However, such a square chip no longer exhibits symmetry with respect to the axis of the cylindrical tube bonded to it.
The absence of axial symmetry and differences of material between the tube and chip in this prior art semiconductor pressure transducer result in false or spurious signals, termed "zero shift", as the static pressure (i.e., common to both surfaces of the diaphragm) or the temperature of the transducer varies. Specifically "zero shift" means a signal that changes as a result of some influence that occurs at zero pressure differential across the transducer diaphragm. Because of this zero shift phenomenon in the semiconductor pressure transducer of the prior art, electronic signal compensation is necessary for the measurement of differential pressures where high accuracy is required.
Accordingly, it is the principal object of the instant invention to provide an improved semiconductor pressure transducer.
Another object of the instant invention is to provide a semiconductor pressure transducer in which the zero shift characteristic is minimized.
Another object of the instant invention is to provide a semiconductor pressure transducer in which spurious signals are minimized.
Another object of the instant invention is to provide a semiconductor pressure transducer capable of measuring pressure differentials with greater accuracy than prior art devices.